The invention relates generally to a device and method for continuously sorting particles and, more particularly, to a device and method for sorting particles through the use of an annular flow chamber and one or more types of separation forces.
Generally, particle separation devices separate particle populations of interest from a suspension and/or other types of particles. The principal method of operation of early particle separation devices relied on a particle""s physical parameters to distinguish that particle from a suspension and/or other types of particles. Examples of these bulk separation techniques include filtration, which is based on particle size, and centrifugation, which is based on particle density. These techniques are effective as long as the particle population of interest is significantly different, with respect to size or density, from the suspension and/or the other particles in the population.
As a subset of bulk separating, continuous separation techniques also exist. The continuous separation of particles in flowing solution requires a well-defined and well-controlled fluid flow pattern. Typically, continuous particle separation devices employ rectangular separation channels. The rectangular geometry of such separation channels results in several advantages including, for example, ease of manufacture, ease of control of fluid flows inside the channels, and ease of design and implementation of forces that drive the separation.
However, rectangular separation channels also suffer from a drawback known as the sidewall effect. The sidewall effect distorts the fluid flow pattern at the side walls of the rectangular separation channel and, hence, adversely affects the performance of the sorting device such as, for example, its resolving power. Hence, it is highly desirable to provide methods and devices for separating particles that do not suffer from sidewall effects and can employ any one of a diverse number of separation forces.
The present invention is particularly directed to continuous particle and molecule separation in flowing solutions. More particularly, the present invention addresses the issue of the sidewall effect by wrapping a separation channel around a cylinder running the length of the channel and by joining the sides of the channel to thereby eliminate any side walls. So configured, the separation channel has an annular cross-section that is enclosed by two coaxial cylinders. Such a transformation leaves the length of the separation channel unchanged with the width of the channel laid on the cylinder. The separation channel width is equal to the difference between the radii of the two cylinder walls bounding the separation channel.
In addition, the present invention generates axially-symmetric separation forces that are coaxial with the annular separation channel to continuously separate particles of interest from a heterogeneous particle population. The heterogeneity can be based on, for example, magnetic susceptibility, particle size, thermal diffusion, phase solubility, and combinations of the preceding. Based on the heterogeneity, a separation force capable of interacting with the separand (i.e., particles subject to the separation process) is provided. The particles or separands can be non-organic (e.g., metals) or organic (e.g. cells, viruses, and molecules including proteins and DNA). The various embodiments of the present invention preferably employ an annular separation channel, an appropriate separation force, and flow compartments. In a first embodiment, an annular separation channel having semi-permeable inner and outer cylindrical walls is used to generate lateral convection forces. In a second embodiment of the present invention, an annular separation channel having heat conductive inner and outer cylindrical walls is used to generate thermal diffusion forces. In a third embodiment, an annular separation channel having non-permeable inner and outer cylindrical walls is used to generate a solubility difference separation force based on solubility coefficient differences between phases of flow compartments. In a fourth embodiment, an annular separation channel having electrically conductive inner and outer cylindrical walls is used to generate an electrophoretic separation force. In a fifth embodiment, an annular separation channel having electrically conductive inner and outer cylindrical walls is used to generate a dielectrophoretic separation force. Yet other embodiments of the present invention provide for the combination of separation forces including lateral convection, thermal diffusion, solubility difference, electrophoretic, dielectrophoretic, and magnetic separation forces.